In a rotary drier, the average retention time of solid is (where Z = length of the drier, metres ρ = apparent solid density, kg/m3 L = flow rate of dry solids, kg/see. m2 drier crosssection H = hold up of solid.) ?
Correct answer: A. Z.H.ρ/L
- A. Z.H.ρ/L
- B. L/Z.H.ρ
- C. H.ρ/L
- D. Z.H/ρL
Explanation
Retention time equals the mass of solids held in the dryer divided by the dry-solids flow rate. For a dryer of length Z, the held-up mass is proportional to ZHρ, giving t = ZHρ/L.
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